Temperature responsive switch device



April 23, 1957 D. w. RICHARDSON EI'AL TEMPERATURE RESPONSIVE SWITCH DEVICE Filed Feb. 23, 1955 FIG. 3

FIG.2

INVEN roRs Malcolm R. Sabiston Douglas W. Richardson United States Patent TEMPERATURE RESPONSIVE SWITCH DEVICE Douglas W. Richardson and Malcolm R. Sabiston, Aurora, Ontario, Canada Application February 23, 1955, Serial No. 490,038

4 Claims. (Cl. 200-114) This invention relates to a temperature responsive switch device and more specifically, to a switch device containing within the organization of operative components, a single pole thermal switch or fuse device electrically in series with a thermostat unit forming a part thereof.

A thermostat may be rendered unresponsive to dangerous temperatures from a number of causes. While a separate fuse is often provided for the electrical circuit served by the thermostat, the latter is located at all times in a temperature sensing position whereby thermal overload can be detected. Thermal overload is primarily the danger circumvented by the use of the thermostat itself. However, in the event of inaccuracy of operation or failure of the thermostat, the danger of thermal overload will arise. Electrical overload can occur independent of thermal overload.

' It is the main object of the invention to provide a safety temperature responsive switch device having a fuse device incorporated in the construction of thermostat components thereof and operative to break the electrical circuit served by the latter with which it is disposed electrically in series, upon thermal overload arising due to incorrect action of the thermostat components and preferably also upon electrical overload occurring in the electrical circuit served by the switch device of the invention.

Other objects of the invention will be appreciated by a study of the following specification taken in conjunction with the accompanying drawings.

In the drawings:

Figure 1 is a plan view of a temperature responsive electrical switch device of the invention;

Figure 2 is an elevation of the device of Figure 1; and

Figure 3 is a partial view of the device of Figure 2 illustrating opening of the single pole thermal safety switch of the invention.

Referring to the drawings, the thermal switch device of the invention is comprised of two main components, a safety fuse device and a thermostat device 11 on the support member of tube 12 which passes through switch arms 13 and 14, bimetal arm 15 and mounting arm 16 near one end thereof, to retain them in spaced apart superposed relationship by insulating means 17 to form a stack type mounting 18 on the base flange 12a of the tube 12. Electrical terminals 19 and 20 are supported in like fashion for each of the switch arms 13 and 14 respectively. However, terminal 20 is electrically isolated in the stack mounting from arm 14. A spring member 21 is supported at one end in the stack mounting 18 in electrical connection with isolated terminal 20 therein and embodies a free portion 22 deflectable against the spring pressure thereof to cause electrical engagement of its otherwise free end 23 to a bar or third terminal 24 in electrical communication with arm 14 in stack mounting 18. The free end 23 of member 21 is preferably retained in electrical engagement with bar 24 by means of an eutectic metal body 25 serving as a thermal fuse 2,790,045 Patented Apr. 23, 1957,

solder. The composition of body 25 is well known and can be ascertained for a particular service from Table II on page 744 under the heading Low melting alloys in Metals Handbook, published by the American Society for Metals, 1948.

The thermostat components shown are of improved and preferred form according to the invention. Switch arm 13 is of the snap acting type in the construction shown, being formed of suitable spring strip metal perforated longitudinally to form spaced apart slots 26 defining a compression strip 27 integrally joined at its ends to tension strips 28 on body sides thereof. The desired snap acting ability is endowed by creasing the tension strips 28 at 28a whereby the length thereof is shortened with respect to that of the compression strip. Accordingly, if the free end 29 of arm 13 is moved upwardly (in the present illustration) to cause the tension strips to pass upwardly beyond the stationary position of adjustment of compression strip 27, the tension strips will draw the free end 29 further upwardly in a snap action.

The compression strip is maintained in an adjustable position by finger 30 formed of an insulating material and projecting downwardly from a bore (not shown) in adjusting screw 31 having reverse thread 32 in fitting 33 on mounting arm 16. Fitting 33 embodies an upwardly projecting stop 34 adapted to be engaged by the stop member 35 spot welded to the shank 36 of adjusting screw 31 thereby limiting rotation of the latter to about 320 degrees to afford correlation of adjustment thereof with action of the thermostat for calibration purposes. Spring 37 avoids thread backlash in action of the adjusting screw while holding to a position of adjustment.

Preferably both upper and lower surfaces of compression strip 27 are positively supported. Accordingly, the invention contemplates the provision of a support member 38 formed of an insulating material and rising from arm 14. The latter is crimped as at 39 or otherwise normally biased in the upward direction. Thus, support member 38 effects the two-fold purpose of supporting compression strip 27 and sewing as a spacer maintaining the desired spaced apart relationship of arms 13 and 14. In this respect, the free end of arm 14 preferably mounts a motion limiting bracket 40 rising above and extending over the free end 29 of arm 13 to mount motion limiting adjusting screw 41 on flange 42 thereof.

A finger 43 of insulating material projects downwardly from screw 41 to limit upward motion of arms 13 relative to arm 14. Arm 15 may be formed to raise its free end 44 responsive to an increase in temperature. It may also be formed to raise the free end 44 thereof responsive to a decrease in temperature. Regardless, motion limiting bracket 39 and arm 14 upon engagement during rising motion of arm 15 will be raised therewith. Contact 45 of arm 14 normally in engagement with contact 46 of arm 13 will raise the free end 29 of the latter to effect snap action of arm 13 opening contacts 45 and 46. The positioning of compression strip 27 by the adjusting means described will determine the amount of motion of actuating button 47 of bimetal arm 15 required for the necessary snap action and hence will determine the temperature at which quick separation of the contacts will occur.

Preferably, fuse device 10 is responsive to both thermal overload and electrical current overload. Assuming that a temperature of 500 degrees Fahrenheit and a current of 10 amperes represent respectively thermal and electrical overload, the metal body 25 would be designed according to the invention to melt at the noted overload temperature. The member 21 at least in that portion adjacent the metal body 25, would be designed to heat to overload temperature when conducting a current of 10 amperes. Accordingly, the fuse device of the invention is responsive to both thermal and current overloads occuring separately or together. After the fuse device has opened as indicated in Figure 3, the spring member 21 can be reset under spring tension while the binding metal at 25 is reheated to retain the spring member in the position indicated in Figure 2.

What we claim as our invention is:

1. A temperature responsive electrical switch device comprising in combination: a plurality of resilient switch arms disposed in superposed spaced apart relationship; temperature responsive means for deflecting at least one of said arms; a support member extending through said arms near one end thereof and including insulating means forming a stack type mounting therefor; an electrical terminal in said mounting for each of said arms, one of said arms being electrically isolated from the terminal therefor; a spring member having one end supported in said stack mounting and having a free portion deflectable against spring pressure to provide electrical connection between said isolated terminal and arm isolated therefrom; and means retaining the free end of said spring arm deflected to maintain said electrical connection below a. predetermined temperature.

2. A temperature responsive electrical switch device comprising in combination: a plurality of resilient switch arms disposed in superposed spaced apart relationship; temperature responsive means for deflecting at least one of said arms; a support member extending through said arms near one end thereof and including insulating means forming a stack type mounting therefor; an electrical ter minal in said mounting for each of said arms; one of said arms being electrically isolated from the terminal therefor; a spring member having one end supported in said stack mounting and having a tree portion deflectable against spring pressure to provide electrical connection between said isolated terminal and the switch arms isolated therefrom; and a binding fuse metal retaining the free end of said spring arm deflected to maintain said electrical connection below a predetermined temperature.

3. A temperature responsive electrical switch device comprising in combination: a plurality of resilient switch arms disposed in superposed spaced apart relationship; temperature responsive means for deflecting at least one of said arms; a support member extending through said arms near one end thereof and including insulating means forming a stack type mounting therefor; an electrical terminal in said mounting for each of said arms, one of said arms being electrically isolated from the terminal therefor; a spring member having one end supported in said stack mounting and having a free portion deflectable against spring pressure to provide electrical connection between said isolated terminal and arm isolated therefrom; means retaining the free end of said spring arm deflected to maintain said electrical connection below a predetermined temperature; and means for heating said retaining means to said predetermined temperature responsive to a predetermined electrical current therethrough.

4. A current overload and temperature responsive electrical switch device comprising, in combination: a plurality of switch arms; a support member extending through said arms near one end end thereof and forming a stack-type mounting disposing said arms in cantilever superposed relationship; means in said mounting electrically isolating said arms; temperature responsive means for deflecting the free end of at least one of said arms; an electrical terminal for each switch arm supported by said mounting and in direct electrical contact therein with the switch arm thereof; an additional terminal supported by said mounting and electrically isolated therein from said switch arms; and a current conducting fuse device including means in said mounting making direct electrical contact with said additional terminal and extending electrically between the latter and one of said terminals to render said switch device inoperative responsive to a current overload independent of said temperature responsive means.

References Cited in the file of this patent UNITED STATES PATENTS 2,518,595 Bletz Aug. 15, 1950 2,522,718 Huck Sept. 19, 1950 2,692,317 Bletz Oct. 19, 1954 FOREIGN PATENTS 718,347 Great Britain Nov. 10, 1954 

